As a method for producing 2- and/or 4-substituted or unsubstituted 1,5-pentanediol derivatives from 2-butenal derivatives, Method (A) is known, in which 2-butenal derivatives are subjected to a reaction with formaldehyde, and the formed intermediates (5-hydroxy-2-pentenal derivatives) are separated from the reaction mixture and then subjected to catalytic reduction [U.S. Pat. No. 3,046,311 (1962)]. However, according to the Examples of said patent, the yield of the intermediate (5-hydroxy-2,4-dimethyl-2-pentenal) based on the consumed 2-methyl-2-pentenal is as low as 63%, and the yield of 5-hydroxy-2-pentenal from crotonaldehyde is only 12%.
Some methods are known for the production of 2,4-dimethyl-1,5-pentanediol; for example, Method (B) in which diethyl methylmalonate and methyl methacrylate, as starting materials, are subjected to a three step reaction and then reduced with lithium aluminum hydride [The Journal of American Chemical Society, 77, 1862 (1955); Chemical Abstracts, 50, 2583d (1956)], Method (C) in which 2-methyl-4-methyleneglutaraldehyde obtained by pyrolyzing 2-ethenyl-5-methylene-1,3-dioxane is subjected to catalytic reduction with Raneynickel as acatalyst [Bulletinde la Societe Chimique de France, 1965, 1355; Chemical Abstracts, 63, 11546e (1965)], and Method (D) in which 2,4-dimethyl-1,4-pentadiene is subjected to hydroboration [The Journal of American Chemical Society, 95, 6757 (1973); Chemical Abstracts, 80, 3372k (1974)]. However, Methods (B) and (D) are unsuitable for industrial application, because expensive reagents such as lithium aluminum hydride and borane are required in the processes. In Method (C), the desired product is obtained only at a low yield.
As a method for producing 2,4-diethyl-1,5-pentanediol, Method (E) is known, in which 3,5-diethyl tetrahydropyran formed by hydroformylation of 2-ethyl-2-hexenol is subjected to catalytic reduction [German Patent No. 2,410,156 (1975); Chemical Abstracts, 84, 43291x (1976)]. However, 2,4-diethyl-1,5-pentanediol is a by-product obtained in the synthesis of 2-ethyl-3-propyl-1,4-butanediol and its yield is extremely low.
As for the production of 5,6-dihydro-2H-2-pyranol, some methods have been reported; for example, Method (F) in which 3-bromotetrahydro-2-pyranol is subjected to a reaction in alcohol in the presence of sodium [Tetrahedron, 18, 657 (1962); Chemical Abstracts, 57, 11150c (1962)], Method (G) in which 5,6-dihydro-2-pyrone is reduced with diisobutylaluminum hydride [Journal of Organic Chemistry, 48, 5170 (1983)], and Method (H) in which 2-hydroperoxy-5,6-dihydro-2H-pyrane is subjected to a catalytic reduction (Japanese Published Unexamined Patent Application No. 101308/78). However, industrial production of 3- and/or 5-alkyl-substituted-5,6-dihydro-2H-2-pyranol derivatives according to the above Methods (F)-(H) is difficult, because raw materials for the synthesis are not readily available. 4-Alkyl-substituted-5,6-dihydro-2H-2-pyranol is described in Japanese Published Unexamined Patent Application No. 101308/78.